Control arrangement for hydraulic systems

ABSTRACT

The return flow passage from the load is connected to a switchover valve, the position of which is controlled by a control flow that is present while the pump is operating. Should the pump be shut off when the control is unintentionally set to lower the load, lowering is prevented by a shut-off member in the switchover valve that is biased to close the return flow passage when the control flow is not present.

United States Patent Comeau et a1.

[ 51 Aug. 29, 1972 54] CONTROL ARRANGEMENT FOR HYDRAULIC SYSTEMS [72} Inventors: Claude Comeau, Bagnolet, France;

Karl-Heinz Digel, Reutlingen-Ohmenhausen, Germany [73] Assigncc: Robert Bosch G.m.b.H., Stuttgart,

Germany [22] Filed: July 6, 1971 [21] Appl.No.: 159,623

30 Foreign Application Priority um July 7, 1970 Germany ..P 20 33 485.4

52 us. 01. ..56/10.2, 137/118, 56/208 51 1111.01. ..A01d 67/00 58 Field of Search ..56/10.2, DIG. 15, 208, 210;

[56] References Cited UNITED STATES PATENTS 3,299,903 l/ 1967 Stacey 1 37/1 18 3,138,908 6/ 1964 Budzich ..56/ 10.2 3,196,599 7/ 1965 Meiners et a] ..56/10.2 3,623,304 11/ 1971 Molzahn ..56/ 10.2

Primary Examiner-Antonio F. Guida Attorney-Michael S. Striker [57] ABSTRACT The return flow passage from the load is connected to a switchover valve, the position of which is controlled by a control flow that is present while the pump is operating. Should the pump be shut off when the control is unintentionally set to lower the load, lowering is prevented by a shut-off member in the switchover valve that is biased to close the return flow passage when the control flow is not present.

4 Claims, 3 Drawing Figures EE i 33 PATENIEDnucza m2 SHEEI 1 0F 2 u ueuraks; Claude c'onsnu Karl Heinz ,D/ GEL nun/cu 3. H

CONTROL ARRANGEMENT FOR HYDRAULIC SYSTEMS BACKGROUND OF THE INVENTION The invention relates to a control arrangement for a load that is fed from a source of hydraulic fluid, the control arrangement having a servo valve spool that in the neutral position closes the connection to the load, in a first work position connects the load to the source of hydraulic fluid, and in a second work position connects the load to the return flow connection. The arrangement further comprises a control passage and a switchover valve for returning the hydraulic fluid from the source back to the source.

The German patent laid open to public inspection No. 1,507,164, FIG. 2, describes a control arrangement in which the hydraulic fluid directlyfrom the pump can be returned in the connection block when it does not pass through a valve to the load. In this case, if a valve is unintentionally operated, the load will sink even when the pump is shut off. It is frequently desired to prevent such lowering of the load when the pump is not operating.

The US. Pat. No. 3,299,903 describes a control arrangement having a plurality of servo valve spools which, to avoid cavitation, controls the return flow from the load in dependence on the feed pressure. Solely for this purpose, there is provided an additional valve that is operated by the hydraulic fluid. The arrangement has no switchover valve.

SUMMARY OF THE INVENTION An object of the invention is to provide, in a control arrangement having a switchover valve, a certain and simple means for preventing lowering of the load when the servo valve spool is unintentionally operated.

Briefly, the invention consists of a load connection, a return flow connection, valve means, such as a servo valve spool, having a neutral position for closing off the load connection, a first work position for connecting the load connection to the source of hydraulic fluid, and a second work position for connecting the load connection to the return flow connection, a switchover valve for returning the hydraulic fluid from the source back to the source, the switchover valve being connected in the return flow connection, control means for operating the switchover valve in dependence on a control flow of hydraulic fluid through the control means, the switchover valve including a shut-off member for closing the return flow connection in the event that the control flow of hydraulic fluid fails.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation,

,together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS F IG. 1 shows in a somewhat simplified form one embodiment of the control arrangement of the invention;

FIG. 2 is a side view of the connection block of the control arrangement shown in FIG. 1; and

LII

FIG. 3 is a longitudinal section taken along line I-I of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to FIG. 1, the control arrangement 10 of the invention comprises a connection block 11, a blocking valve 12 for a single acting load 13, and an end plate 14.

In the following explanation of the connection block 1 1, reference is made to FIGS. 2 and 3. The connection block 11 has a housing 15, which incorporates a first bore 16 that has a conventional relief valve 17. The pressure relief valve 17 protects a feed connection 18 from a return connection 19. In the housing 15, there extends at right angles to the first bore 16 a second bore 21, which passes through a first chamber 22 and a second chamber 23. A shut-ofi member 24 is free to slide in a fluid-tight relationship in the second bore 21. The member 24 is part of a switch-over valve 25. A spring 26 pushes the shut-off member 24 into a first, rest, position that is defined by a spring washer 27. In this position, a first piston-like section 28 of the member 24 separates the feed connection 18 from the first chamber 22. In this position of the shut-off member 24, a second piston-like section 29 of this member separates the second chamber 23 from the first chamber 22.

The spring 26 is located in a chamber 31, from which latter a control passage 32 leads to a flange face 33. A pressure regulating valve 34, which is incorporated in the shut-off member 24, connects the chamber 31 with the feed connection 18, which leads to the flange surface 33. A pump 35 forces hydraulic fluid from a tank 36 into this feed connection 18. A return flow connection 37, which is connected to the second chamber 23, also leads to the flange surface 33.

The blocking valve 12, which is shown in FIG. 1 in a somewhat simplified form, is a conventional valve for controlling the single acting load 13. The servo valve spool 39 of the blocking valve 12 has three different positions: a neutral position 41, a raise position 42, and a lower position 43, whereby a load connection 44 can be hydraulically shut off or connected to a feed connection 45 or connected to a return connection 46. When the servo valve spool 39 is in the raise position 42, it also shuts off a control connection 47 for the switchover valve 25. When the servo valve spool is in either of the other two positions 41 and 43, it opens this control connection 47. The feed connection 45, the return connection 46, and the control connection 47 in the blocking valve 12 begin at the flange face 49 of the blocking valve, this flange face being continuous with the end plate 14. These connections, or passages, 45, 46, 47 are connected in the flange face 48 with the corresponding connections, or passages, 18, 37, and 32 in the connection block 11. The feed connection 45 and the return connection 46 are closed by plugs 51 in the flange face 49.

The end plate 14 is a flange-connected to the flange face 49 of the blocking valve 12, the end plate 14 incorporating a discharge connection 52, which connects the control connection 47 of the blocking valve 12 to the tank 36.

The pressure regulating valve 34, the control connection, or passage, 32 and 47, and the discharge connection, or passage, 52 constitute the control connection, or passage, 53 of the switchover valve 25.

The arrangement just described operates in the following manner. If the servo valve spool 39 of the blocking valve 12 is in the illustrated neutral position 41, the load 13 is hydraulically locked, and the control connection 47 is turned on. If the pump 35 pushes hydraulic fluid through the feed connection 18, a control flow of hydraulic fluid moves through the control passage 53 into the tank 36. The pressure fall across the pressure regulating valve 34 keeps the switchover valve 25 open, and the largest part of the hydraulic fluid moved by the pump 35 flows through the return connection 19 to the tank 36.

If the servo valve spool 39 is moved to the raise position 42, the control passage 53 is interrupted so that the switchover valve 25 makes the connection to the return connection 19. Thus, hydraulic fluid flows from the feed connection 45 to the load 13.

If the servo valve spool 39 is moved to the lower position 43, the hydraulic fluid flowing back from the load 13 passes through the return flow connection 37 and the chamber 23 of the connection block 11. Provided that the pump 35 is operating, the switchover valve 35 is opened, and the pump 35 can discharge into the tank 36, while a small control flow passes through the control passage 53 to the end plate 14, where it discharges into the tank 36. At the same time, the shut-off member 24 provides a connection from the chamber 23 to the return connection 19, so that the load can lower.

However, if the pump 35 is shut off and the servo valve spool 39 is unintentionally moved to the lower position 43, no control flow moves trough the control passage 53. The spring 26 holds the shut-off member 24 of the switchover valve 25 in the first, rest, position, in which the piston-like section 29 of the member 24 separates the chamber 31 from the return connection 19. In this way, there is prevented an undesired lowering of the load 13 when the pump 35 is shutoff.

The control arrangement of the invention can be constructed as a plurality of control valves.

The control arrangement of the invention can be used with a harvester thresher, the load 13 operating the cutting table of the thresher.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above.

While the invention has been illustrated and described as embodied in a control arrangement for hydraulic systems, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and r e of e uivalence of th followin claims.

wriii is claii ned as new an; desired 0 be protected by Letters Patent is set forth in the appended claims:

1. A control arrangement for a hydraulic load that is supplied with hydraulic fluid from a source, comprising, in combination, a load connection; a return flow connection; valve means having a neutral position for closing off said load connection, a first work position for connecting said load connection to the source of hydraulic fluid, and a second work position for connecting said load connection to said return flow connection; a switchover valve for returning the hydraulic fluid from the source back to the source, said switchover valve being connected in said return flow connection; control means for operating said switchover valve in dependence on a control flow of hydraulic fluid through said control means, said switchover valve including a shut-off member for closing said return flow connection in the event that said control flow of hydraulic fluid fails.

2. The control arrangement as defined in claim 1, wherein said shut-off member moves between a first position in which said return flow connection is closed and a second position in which said return flow connection is open, and further including resilient means for biasing said shut-off member to said first position when said control flow of hydraulic fluid falls.

3. The control arrangement as defined in claim 1, further including a plurality of control valves; a relief valve connected to the source for controlling the pressure of the hydraulic fluid therefrom; and connection block means for incorporating said relief valve and said switchover valve.

4. The control arrangement as defined in claim 2, as used with a harvester thresher, said switchover valve being connected to the means that operates the cutting table of the harvester thresher. 

1. A control arrangement for a hydraulic load that is supplied with hydraulic fluid from a source, comprising, in combination, a load connection; a return flow connection; valve means having a neutral position for closing off said load connection, a first work position for connecting said load connection to the source of hydraulic fluid, and a second work position for connecting said load connection to said return flow connection; a switchover valve for returning the hydraulic fluid from the source back to the source, said switchover valve being connected in said return flow connection; control means for operating said switchover valve in dependence on a control flow of hydraulic fluid through said control means, said switchover valve including a shut-off member for closing said return flow connection in the event that said control flow of hydraulic fluid fails.
 2. The control arrangement as defined in claim 1, wherein said shut-off member moves between a first position in which said return flow connection is closed and a second position in which said return flow connection is open, and further including resilient means for biasing said shut-off member to said first position when said contrOl flow of hydraulic fluid fails.
 3. The control arrangement as defined in claim 1, further including a plurality of control valves; a relief valve connected to the source for controlling the pressure of the hydraulic fluid therefrom; and connection block means for incorporating said relief valve and said switchover valve.
 4. The control arrangement as defined in claim 2, as used with a harvester thresher, said switchover valve being connected to the means that operates the cutting table of the harvester thresher. 